Our Backyard | Scale back in the garden

The pest insect that I have noticed in prolific numbers this year on many trees is scale.

The hot dry conditions we have been experiencing are ideal conditions for the increased numbers on our plants.

Scale are a shell-like, waxy insect that feeds off the sap of your plants. This season, I have noticed scale on fruit trees, Cercis 'Forest Pansy', a few different varieties of silver birch, some ornamental shrubs and native trees and shrubs.

Scale insects can be difficult to see and look more like a growth than a bug. They look like a small brown bump and they don't move. They closely resemble a scab. They are rounded, oval or flat shaped and can range in size from barely visible to large bumps. Their colour can range from brown and tan to orange or even white.

CAMOUFLAGE: Scale insects can be difficult to see and look more like a growth than a bug.

CAMOUFLAGE: Scale insects can be difficult to see and look more like a growth than a bug.

SPOTTED: Scale like to cluster together, so once the population gets large they are easy to see.

SPOTTED: Scale like to cluster together, so once the population gets large they are easy to see.

They do like to cluster together, so once the population gets large they are easy to see.

There are many stages in the scale insect life cycle and the whole cycle takes about seven to 10 weeks. The eggs take a few weeks to hatch in nymphs (these can crawl) and then six to nine weeks for the crawlers to mature into adults.

The female crawlers can move around on the plant or move to surrounding plants. Once an adult, they can no longer move. Scale insect eggs and nymphs are tiny, which is why its so simple for scale populations to get out of hand before you notice them.

Male crawlers and adults are tiny, flying, gnat like insects that fly around looking for females to mate with. Scale can go through one or two generations each year.

Scale will seriously weaken and sometimes kill your plants if the infestation becomes too great. Scale can result in stunted or deformed leaf growth, yellowing of the leaves, brown pock marks and even leaf drop.

Scale generally infest branches, stems and leaf joints and sometimes along the veins of leaves, but you can find them anywhere on the plant.

Plants covered in scale may have a sticky appearance on the leaves. This can be a good way to identify scale if you are not sure what is wrong. As scale feed they excrete a sticky residue which is a common sign of infestation. This sticky residue is known as honeydew and is a mixture of undigested sugar and water passed through the insects digestive system and then deposited onto the leaves and stems of the plant.

Honeydew attracts other insects such as ants, which is another way to identify scale on the plant.

Honeydew may also encourage a fungus called sooty mould that will give the plant a black 'sooty', appearance. On scale-infested trees and shrubs you will notice a black residue all over the ground underneath them.

Scale can be treated in a number of ways. Maintaining the good health of your garden can help with this. Lady beetles can attack and significantly reduce scale insect populations.

When scale insect populations are not out of control and can be reached, its worth picking them off by hand. If a branch is heavily infested it may be worth cutting the branch off and discarding away from the garden.

Sometimes infestations are too great and chemicals are required. Rather than spraying, I like to use a tablet, inserted into the ground. White oil (pest oil) is also effective as a control measure.

I find if you are vigilant and keep and eye on your plants, you can wipe scale off your plants as they appear. Then you can avoid infestations and chemicals.

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